There exists in the prior art a multitude of positive displacement pumps, each of which are adapted to receive fluid from an inlet line and discharge the fluid into an outlet line at an increased pressure level. In most prior art positive displacement pumps, a blockage in the outlet line creates an excessive pressure build-up within the pump housing which typically causes the pump motor to overheat and eventually fail. Small pumps incorporating small, light duty motors are particularly prone to such overheating and failure during occurrences of outlet line blockage.
To aid in the prevention of pump motor overheating and failure, it has become a common practice in the prior art to insert a pressure relief valve into the outlet line of the pump to prevent the fluid pressure within the pump housing from exceeding a predetermined maximum level. However, this prior art method of providing pressure relief subjects the pump to a maximum change in pressure at the highest work output of the pump motor (which is non-productive due to the outlet line blockage), thus putting considerable strain on the motor and leading to accelerated wear and failure.
In addition to the foregoing, the prior art positive displacement pumps are generally configured to function in only a single operational mode. In this respect, the modification of the operational characteristics of the pump generally requires the performance of retrofit procedures which are both time consuming and expensive. In view of the difficulties associated with such pump modifications, a required change in the operational characteristics of the pump typically necessitates the replacement of the entire pump rather than attemptzing to modify the same.
The positive displacement pump constructed in accordance with the present invention is intended to overcome the deficiencies associated with similar prior art pumps. In particular, the present pump incorporates a modular pump component which is selectively insertable into and removable from within the pump housing and adapted to modify the operational characteristics of the pump when inserted into the housing. The modular pump component may comprise an unloader valve which reduces the change in pressure within the housing to zero in the event of an outlet line blockage and allows the pump motor to go into a free run condition thus prolonging its useful life. Alternatively, the modular pump component may comprise a motor speed control valve which is adapted to decrease the rotational speed of the motor proportionally to increases in the fluid pressure in the housing, and increase the rotational speed of the motor proportionally to decreases in the fluid pressure in the housing.